Generally, an insert is fastened to a cutting tool mounted on a machine tool, to be used for cutting a workpiece composed of ferrous, nonferrous metals, nonmetal materials, and so on.
Such insert generally includes a body, a cutting portion provided on an upper surface edge of the body to directly cut the workpiece, and a fastening portion provided on the body to be fastened to a holder of the cutting tool. Specifically, the cutting portion includes first and second major cutting edges respectively formed on two long edges of the rectangle-shaped upper surface of the body, and first and second minor cutting edges respectively formed on two short edges. The fastening portion includes first and second fastening holes extending through the body from the upper surface to a lower surface. Further, to enable turning by 180 degrees and re-use thereof, the first and second major cutting edge, the first and second minor cutting edges, and the first and second fastening holes respectively have symmetric shapes by 180 degrees with reference to a center of the upper surface.
Meanwhile, the tool holder generally includes two or more chip pockets having a pocket-shaped flute to discharge chips, a sheet portion provided at each of the chip pockets to fasten the insert, and a web forming a boundary between the first and second pockets.
One of related insert routers is disclosed in U.S. Pat. No. 5,893,683, which has a structure such that, as illustrated in FIGS. 9B and 9C, a lower surface 41 of the insert 28 has a flat shape, and as illustrated in FIG. 8, a lower surface sheet portion 26 of the tool holder fastened with the lower surface 41 of the insert 28 has a correspondingly flat shape. Further, as illustrated in FIGS. 9B and 9C, a major edge clearance surface 45 that forms a major side surface of the insert 28 is inclined with respect to the upper surface 32 and the lower surface 41, while forming a flat plane. Further, as illustrated in FIGS. 8 and 9A, 9B and 9C, a blind groove 44 to enhance fastening torque with the tool holder is formed between the first and second fastening holes 42, in which the blind groove 44 has a closed shape such that the blind groove 44 is not extended through to the upper surface 32, but formed in a portion of the lower surface 41.
However, the related technology described above has a problem of deteriorated fastening torque among parts, allowing the insert 28 to be escaped out of the tool holder, because the lower surface 41 of the insert 28 where the insert 28 and the tool holder are in contact, and the lower surface of the tool holder each have the flat shapes.
Further, since the major edge clearance surface 45 of the insert 28 forms a flat plane, it does not have a part that can serve as a locking portion such that the insert is escaped from the tool holder when subject to centrifugal force or centripetal force during cutting process, which is problematic.
Further, in order to coat the insert 28, two pins (not illustrated) are inserted into the first and second fastening holes (see 42), respectively, after which the insert 28 is loaded into a coating furnace (not illustrated) for coating thereof. During this process, as one insert 28 occupies two pins, the charge decreases considerably.